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Principal vs. principle

As a noun, principal refers to (1)one who holds a presiding position or rank, and (2) capital or property before interest, and it’s also an adjective meaning (3) first or most important in rank. The head of a primary or secondary school is a principal.

Principle is only a noun. In its primary sense, it refers to a basic truth, law, assumption, or rule.

Though the words sound alike and share a distant origin in the Latin princeps (meaning first or original), they come from separate French sources and have always been different words in English.1